The present invention relates generally to abrading tools. More particularly, the invention is concerned with an abrasive member for surfacing a workpiece by rotary abrasion.
The surfacing of relatively hard materials such as granite, marble, limestone, concrete, artificial stones, ceramics and hard resins involves several operations. These include lapping, grinding, finishing and prepolishing of the stone surface. The lapping operation comprises bringing down to level a surface lying slightly above another one on a flat surface, and removing marks caused by wiresawing. Small cavities formed in the surface by the lapping operation are then removed by grinding. In the finishing operation, scars left by the grinding operation are removed. The prepolishing operation enables one to eliminate scars having a depth of 4 to 10 microns left by the finishing operation, before the final polishing of the surface with tin or aluminum oxide to achieve the desired glossy finish.
The above operations are generally carried out using an abrasive disc driven by a hand-held, electrically or pneumatically powered tool. Where the workpiece to be surfaced is a slab or floor, use is preferably made of a plurality of abrasive pads mounted on a horizontal turntable. In either case, a center water feed is usually provided to eliminate grinding dust and reduce the health risks associated therewith, while ensuring proper cooling. However, sludge buildup often occurs, causing loading of the abrasive disc or pad.
In order to remove the waste grinding liquid, it has been proposed in U.S. Pat. No. 4,918,872 to secure a plurality of grinding wheel segments in a predetermined arrangement to a rotary driving platen so as to form a plurality of surface grooves extending in a generally radial direction and away from the direction of rotation of the grinding wheel segments, from the inner side toward the outer periphery of the arrangement of segments. Such grooves are effective for removing only part of the waste grinding liquid and are thus unsatisfactory for a complete scavenging of detritus.
U.S. Pat. No. 4,037,367, on the other hand, has proposed rotary grinding disc featuring a network of grooves having a pattern selected to include the mirror image of the sequence of repeating lines or curves, with a view to improving the scavenging effectiveness regardless of whether the disc rotates clockwise or counterclockwise. However, the curvature of the grooves and the criss-crossing thereof are such as to cause accumulation and packing of detritus at the intersections of the grooves. Moreover, since the quadrilateral-shaped working elements which are formed by the network of grooves have sidewalls perpendicular to the surface of the workpiece, chipping of the workpiece often occurs upon impact of the leading sidewalls of the working elements with surface irregularities protruding from the workpiece.